1. Field of the Invention
Embodiments of the disclosure relate to a liquid crystal display capable of operating in an impulse drive manner.
2. Discussion of the Related Art
Active matrix type liquid crystal displays display a motion picture using a thin film transistor (TFT) as a switching element. The active matrix type liquid crystal displays have been implemented in televisions as well as display devices in portable devices such as office equipments and computers, because of the thin profile of the active matrix type liquid crystal displays. Accordingly, cathode ray tubes (CRT) are being rapidly replaced by active matrix type liquid crystal displays.
A motion blur phenomenon occurs in which a motion picture displayed on the screen of a liquid crystal display is not clear and blurry because of hold characteristics of a liquid crystal material. When comparing the liquid crystal display with a cathode ray tube (CRT), as shown in FIG. 1, the CRT provides data to cells by causing a phosphor to emit light for a very short period of time to display an image in an impulse drive manner. On the other hand, as shown in FIG. 2, the liquid crystal display supplies data to liquid crystal cells during a scan period and then holds data charged to the liquid crystal cells during a remaining field period (or a frame period) to thereby display an image in a hold drive manner.
Because the CRT displays the motion picture in the impulse drive manner, a perceived image that a viewer perceives becomes clearer as shown in FIG. 3. On the other hand, as shown in FIG. 4, light and darkness of a perceived image that a viewer perceives are not clear and blurry because of the hold characteristics of the liquid crystal material in the motion picture displayed on the liquid crystal display. A difference between the perceived images of the CRT and the liquid crystal display is caused by an integral effect of an image temporarily held in eyes following a movement. Accordingly, even if the liquid crystal display has a fast response time, the viewer watches a blurry image because there is a difference between the movement of the eyes and a static image of each frame.
A method for driving the liquid crystal display in an impulse drive manner, for example, a black data insertion (BDI) method has been proposed so as to improve the motion blur phenomenon in the liquid crystal display. In the black data insertion method, the liquid crystal display provides video data on the screen of the liquid crystal display and then supplies black data to the screen, and thus can be driven the an impulse drive manner.
The black data insertion method is a method capable of obtaining an imaginary impulse drive effect by inserting black data between video data to be displayed. Because the black data is inserted between the video data to be displayed in the black data insertion method, a luminance reduction and a flicker of an image displayed on the liquid crystal display occur. If the liquid crystal display is driven at a frame frequency of 120 Hz, the problem of flicker in the black data insertion method has been improved. Further, the luminance reduction does not greatly affect most of liquid crystal displays except some of liquid crystal displays requiring a high luminance. FIG. 5 illustrates an example of driving a liquid crystal display at a frame frequency of 120 Hz without black data insertion. FIG. 6 illustrates an example of driving a liquid crystal display at a frame frequency of 120 Hz in a black data insertion manner.
The liquid crystal display inverts a polarity of a data voltage to be charged to liquid crystal cells every one frame period, so as to reduce direct current (DC) image sticking and to prevent degradation of liquid crystals. In a normal drive method in which the black data is not inserted, a polarity of a charge voltage (i.e., the data voltage) of the liquid crystal cells is inverted every one frame period as shown in FIG. 7, and thus a positive polarity data voltage and a negative polarity data voltage are cancelled each other out. Hence, a polarity deflection does not occur. On the other hand, in the black data insertion method, when the polarity of the data voltage of the liquid crystal cells is inverted every one frame period as shown in FIG. 8, the black data is repeatedly inserted as a voltage having the same polarity. Accordingly, as shown in FIG. 9, the black data insertion method generates a residual voltage in the liquid crystal cells because of the polarity deflection of the black data voltage, and as a result, the image sticking occurs.